You could swap double team for dig (attack, 80) or brick break (attack, power 75). Even though Brick Break is less powerful by five, your foe can't just switch out to a flying Pokemon and make it useless like they can with Dig.

Alrighty, it's been a few days since I've recommended some movesets. Glad to be back in the swing of things!

Floatzel is born to be a Physical Sweeper. It can't really do anything else (Besides revenge killing, which it is also incredibly good at doing). The aim for a good Floatzel Moveset is full-out attack, with a bit of buffing and boosting for support.

Aqua Tail/Waterfall
(Waterfall for reliability and flinching, and Aqua Tail for raw power. Both are great attacks, and it's up to you for which one you pick)

Ice Punch
(Try your very hardest to get Ice Punch on Floatzel. It compliments its Attack stat, and hits Flying, Ground, Dragon, and Grass types, which are all of Floatzel's biggest worries. Not just because of weaknesses, resistances, etc, but because of the natural advantages they'll usually have over him)

Brick Break/Rock Tomb/Iron Tail/Dig
(Use one of these for some added coverage. Brick Break gets Physically inclined Steel walls out of the way, Rock Tomb can get Bug, Flying once again, and Ice types, Iron Tail can also hit Ice types, and also gets Rock. Not much of a big deal there though. FInally, Dig is probably the worst choice, at first glance, but it's your only counter toward an Electric-type. Use whichever one you want)

Bulk Up
(One of the few Non-Fighting-Type Pokemon to learn Bulk Up. It raises your ability o be a good Physical Tank, so it's a great buff to have on Floatzel, for both the Attack boost and the Defense boost. If you want all attacking moves though, pick one of the leftover three attacks from above)

Floatzel is a great Pokemon. Not just for its good Attack and Speed stats, but for its general versatility and rather varied movepool. Jut like with Porygon, it has a somewhat small movepool, but the movepool fits Floatzel like a glove, being able to efficiently utilize any attack or move it can learn. The possibilities are nearly endless with a Floatzel, but it's best Niche lies in the Physical Sweeper, where it can put its Base 105 Attack and Base 115 Speed stats to good use.

EDIT: How could I forget? If you can't get Ice Punch on Floatzel for whatever reason you may have, just get a Heart Scale, find the fat Move Rememberer(?) guy and get Floatzel to remember Ice Fang.

Surf: STAB, good power, high accuracy.
Ice Beam: Good power, chance to freeze, high accuracy, deal with Grass types.
Taunt: Stops the foe from using Stat moves.
Rain Dance: Increases Floatzel's Speed and increases the power of Surf.

I've been called an idiot when I go all Choice Band + Blizzard on people, but Ice Fang doesn't KO jack crap. Blizzard has a large enough BP difference to do much more damage. If ran with rocks, it can probably KO Dragonite / Flygon / Salamence / Landorus and maybe even Gliscor. Which rocks! Waterfall is his main attack. I personally use Hasty, although Mild helps Blizzard get easier guaranteed KO's on those quad effective receievers.
Brick Break and Crunch gives amazing coverage together.

As someone who has two floatzel one a special sweeper the other a physical
If it has a nature that boosts attack it should have
Low kick
Aqua jet/ waterfall / Aquatail
Crunch / iron tail
And the most important move on this set ICE PUNCH

Because of its plausibly high Speed stat (second fastest Water-type behind Greninja by 8 points), and relatively high Attack stat, I guess you could say that Floatzel could be a potentially good start-of-battle sweeper. Add Rain Dance to that mix (assuming the Floatzel has Swift Swim), than practically nothing can outspeed Floatzel, other than Agility-users. The only problem with Floatzel is its rather poor defensive stats, and its rather limited movepool. But it is still extremely useful for Rain teams.

Here's my suggestions:

Nature: Jolly (or much less desirably Adamant)
Ability: Swift Swim

Moveset:
-Rain Dance - pretty obvious why.
-Waterfall - STAB and possible flinching
-Ice Fang - type coverage. If you work hard enough to get it Ice Punch, that would be more favorable. Don't waste Ice Beam with Floatzel; its Attack stat is too good to be training Special Attack.
-Crunch, Brick Break, or (less favorably) Dig - more type coverage.
-Double Team might also be consideration if you're not using Pokémon Showdown

As for items, I have multiple suggestions:
-Focus Sash - because of Floatzel's poor defensive stats
-Water Gem - boosts whatever Water type move you want to use, especially in rain
-Damp Rock - for obvious reasons
-Eject Button - if you'd rather have something else use the rain (Politoed with Drizzle might be more appropriate, unless you aren't attacked immediately and would like to use the Swift Swim benefits)

One of the fastest Water Type Pokemon, Floatzel! it is a Physical Pokemon so to bad Surf and Ice beam can't be very effective since..yeah cause that would be perfect,To bad with low Defense of 55 and Special Defense of 50, Floatzel won't stay in for long so pretty Much just give it a Focus Sash, anyway heres a set that I hope that will work!

Waterfall is the best Physical watertype move for Floatzel and all physical water type Pokemon and has a 30% chance of fliching the opponent and so that will make up for Floatzel staying in longer, Oh and STAB. Ice Fang is for Grass coverage and a small chance of frezzing the opponent wich again will make it up for Floatzel staying in longer. Rain Dance is for activaiting its abilities so if it has Swift Swim it'l raise its speed by 2 stages wich is good if you are running on a Adamant Nature and Water Veil to curenit from those nasty Burns, Rain dance will also make its water type moves a little more powerful. Aqua Jet is a priority move so it may almost always goes first go first wich is good if the opponent is low on HP or you can go with Crunch that does good power and has a chance of lowering Defense stat wich can make you hit them harder.